GSD3 is an inherited disorder that causes a buildup of glycogen in certain organs and tissues – especially in the liver and muscles. It is caused by mutations in the AGL gene leading to a deficiency in the debrancher enzyme, key in the breakdown of glycogen. It is inherited in an autosomal recessive manner. Symptoms typically present in infancy, but may only occur in adulthood.

Children are often diagnosed because they have been noticed to have a swollen abdomen due to a very large liver. Patients may also have low blood sugar, a high level of fats in the blood and delayed growth. Symptoms related to liver disease and progressive cardiac and skeletal muscle involvement vary in age of onset, rate of disease progression and severity.

Individuals with GSD3 vary remarkably depending on which sub-type they have – 3a, 3b, 3c and 3d.

GSD 3a is the most common type (85%) and affects both the liver and (cardiac and skeletal) muscles. GSD 3b affects about 15% of individuals, and only affects the liver. GSD3c and 3d are extremely rare.